Pie, when he came to me, had no forward - his trot was a kind of short-strided shuffle. Forward is now very well established, with the assistance of secondary cues, and he's now sensitive to changes of energy that allow him to respond very well to requests for long and short trot. His softening work is progressing - his connection/feel is good, he backs extremely well just with my barely taking any drape out of the reins, and his walk and trot softness are greatly improved and canter is starting to take shape. But he still has a tendency to "dive" - when asked to soften he drops his head and neck very low and sometimes goes behind the vertical.
And, although he sidepasses beautifully - he came to me with this, as well as pretty nice turns on the forehand and haunches - there are some things going on in our riding that I need to work on. When cornering, he tends to want to drop his hindquarters to the inside, and doesn't respond well to leg aids to move his hindquarters out, which seemed odd to me considering how responsive he is in sidepass. I suspect it's because he hasn't generalized - he thinks that the leg aid at the girth means sidepass - at the walk - and leg aid behind the girth means turn on the forehand. Period.
Pie also has some conformational challenges. He's got legs, feet and hindquarters that are pretty good - his hind leg angulation is just about perfect, and his feet, leg bone and joints are large and solid. But he's narrow through the body and tends to carry his hind legs in particular very close together. His shoulder is upright enough that he's never going to have great extension of the front legs - he wouldn't make a very good dressage horse. And he's long - in the neck and body both, with a large and heavy head, and he's built somewhat downhill, although that's improved as he's grown up. All of these defects make it harder for him to carry himself from behind, and make it harder to influence one part of his body without it becoming isolated from the rest of him.
Dawn and Red are both very square and compact, with good sloping shoulders and very good hind leg angulation. Dawn, like Pie, is somewhat downhill, and this has been her primary challenge, but she's well on the way to overcoming it, although she's never going to have great extension. Red's conformation is just about darn perfect in every respect, very uphill, with excellent angles - he'd make a dandy dressage horse, or just about anything else requiring athletic ability. It's a lot easier to keep Dawn and Red "together" - what's referred to (somewhat of a misnomer) as "in front of the leg", which means that the front end and hind end stay connected and work together, and the horse is carrying herself from behind. (Red's issues with a disconnected and rubbery head and neck when I got him are almost all gone now, and we believe were due to excessive lateral flexion work.) Pie doesn't have these advantages.
I've been thinking about this for a while, and some things became clearer to me yesterday - I checked some things out. I moved my Western saddle back a bit (the About the Horse saddle can sit farther forward than most Western saddles due to the shoulder flare of the tree, and I'd been tending to do this with Pie to compensate for his downhill build), so I'd be farther towards his hind end. Pie and I did a lot of our trot and canter warm up on a loose rein, and although he tended to invert his head and neck (I ignored this), he was carrying himself from behind and corners were pretty good if I directed him with my focus. As soon as I asked him to soften at the trot or canter, he wanted to dive, and I lost the ability to direct the hind end unless I put my inside leg way back - to the back cinch - and even then it was hard for him to respond - he was basically falling on the forehand and trailing the hind end. The more forward he had, the worse the hind end issues became, even when he was carrying himself well from behind - he became less able to respond to the leg asking him to move his hindquarters over - this is typical with a gap in understanding - it tends to become worse with increasing speed.
I think he really doesn't understand leg aids - with the exception of his basic lateral work (sidepass, turns on the haunches and forehand) - he thinks of leg as meaning only forward. More leg, anywhere, means more forward. Dawn had this issue too, but now accepts (some) leg as support and direction - we're still working on this. And there's the issue of the front disconnecting from the back end as well to deal with - it's all related. This is a hole in our training, and it's time to get it remedied.
So, here's the plan for now. I'm going to switch Pie back into my dressage saddle for some of our arena work, which gives me a slightly better saddle position and flexibility for my leg position. I'm going to do some in-hand work to help him understand the leg aids and how to move his hind end in response to leg aids, so he'll have something to generalize from - he's a horse who tends to say "I learned it this way, and that's the way it is." We'll be doing more loose rein work so that I can work on riding the hind legs, while ignoring the head and neck. Lots of transitions, including ones to develop carriage from the hind end, like backing into immediate trot. And we'll be doing lots of exercises involving moving the hind end - spiral in/out and shoulder in - starting at the walk and only progressing to trot once he's got the idea, and making sure what we're doing is correct and the the hind end is the engine and that he's staying connected from back to front (not the other way around). Pie's very smart, and once he gets it, I think things will improve quickly. I also expect improving this issue with the hind end will help a lot with his front end issues, such as diving when softening - he'll be carrying himself better from behind, which should automatically elevate the front end and keep the whole horse connected.